thunk: clear thunk instance payloads

Since thunk instances are utilized via initializer functions
which always initialize all the environment members, it made
sense to use plain malloc().

But with the addition of payloads, there's a component of the
allocation which gets split out for the caller to make use of
in a much more ad-hoc fashion.

In my personal programming style, I tend to take advantage of the
assumption that allocations are zeroed.  The returned payload is
essentially used as a heap allocation, just coupled to the thunk
instance in terms of life cycle.  So I prefer the payload space
be zeroed on allocation.

Since it still seems sensible to leave the thunk's environment
part of the instance exclusively initialized by it's init
function, this commit leaves the plain malloc and just memset's
the payload when present.

1 files changed, 7 insertions, 2 deletions

diff --git a/thunk.h b/thunk.h
index 7fbdfbd..262137f 100644
--- a/thunk.h
+++ b/thunk.h
@@ -21,6 +21,7 @@
 
 #include <assert.h>
 #include <stdlib.h>
+#include <string.h>
 
 typedef struct thunk_t thunk_t;
 
@@ -488,8 +489,10 @@ struct thunk_t {
 		env = malloc(sizeof(*env) + payload_size);			\
 		assert(env);							\
 										\
-		if (payload_ptr)						\
+		if (payload_ptr) {						\
+			memset(env->__payload, 0, payload_size);		\
 			*payload_ptr = env->__payload;				\
+		}								\
 										\
 		env->__thunk.dispatch = __thunk_dispatch_##_name;		\
 										\
@@ -566,8 +569,10 @@ struct thunk_t {
 		env = malloc(sizeof(*env) + payload_size);			\
 		assert(env);							\
 										\
-		if (payload_ptr)						\
+		if (payload_ptr) {						\
+			memset(env->__payload, 0, payload_size);		\
 			*payload_ptr = env->__payload;				\
+		}								\
 										\
 		env->__thunk.dispatch = __thunk_dispatch_##_name;		\
 										\